The present invention is related to a process for producing inorganic porous materials and to materials prepared by such process. These materials are favorably applied to producing columns for chromatography, porous filters for separating blood, porous catalysts, or enzyme supports. Such inorganic porous columns can be favorably applied to liquid- and gas-chromatography. These columns can be used unmodified or modified e.g. by covering their surface with molecules like hydrophobic hydrocarbon ligands (e.g. octadecyl ligands) or like hydrophilic ligands like 2,3-dihydroxypropyl derivatives. The ligands of such modified columns can be further modified using known procedures. Porous catalysts or enzyme supports can be prepared by adding enzymes, e.g. glucose isomerase, or catalytic metal elements, e.g. platinum and palladium. Such inorganic porous columns can also be attached to an injector or a catheter for blood injection.
The sol-gel method is one of liquid phase reaction paths to produce inorganic porous materials, especially silica gels. The sol-gel method denotes widespread processes in which polymerizable low molecular weight species are first generated, and through polymerization reactions, aggregated or polymerized materials are finally obtained. For example, the sol-gel method can be applied by hydrolyzing metal alkoxides, metal chlorides, metal salts or coordinated compounds which typically contain carboxyl or beta-diketone ligands. A process of this kind is disclosed in EP 0 363 697. In this process an organic polymer is used, which is compatible with the solution of the metal alkoxide or its polymer, and which undergoes phase separation during the hydrolysis-polymerization step. The materials produced by this process display connected open pores with a narrow range of the pore size distribution.
In applying porous materials as support or separation devices, the average size and size distribution of pores should be precisely controlled so as to optimize the function of supported substances or the separation efficiency. Accordingly, there have been numerous trials to control the size and distribution of pores by adjusting the reaction parameters of gel preparation. For many applications the porous shaped body should contain defined mesopores in addition to the network of macropores present. Thus the usable inner surface would be enlarged, and distances to be traversed by diffusion minimized.
Typical chromatographic columns widely used are classified into two groups; (a) organic packed column or rod column typically composed of styrene-divinylbenzene copolymers, and (b) inorganic packed column typically composed of silica gel beads.
Organic columns are disadvantageous in the points that: (a) applicable pressure is low due to their low mechanical strength, (b) they swell or shrink on contacting organic solvents, and (c) they cannot be disinfected by heating up to high temperature. Inorganic column materials are free from these disadvantages, and among others silica gels are most widely used.
Conventional inorganic packed columns, however, have some disadvantages different from those of organic columns. That is, columns composed by packing inorganic beads into a cylinder exhibit a high flow resistance and, consequently, the pressure depression is large. As a result, the flow rate decreases and it requires a long time to accomplish the analysis. At the same time, these columns are hard to be used by attaching the injector handled with human hand, because the flow rate becomes so low.
Also, since the sample flow depends on the packing condition, the analysis results tend to scatter when analyzed with several columns with different manufacture lots. Moreover, when the packed columns are attached to an injector or a catheter for blood injection, the packed beads may come out by some accident.